The general purpose of this project is to explore the molecular basis of active transport in microorganisms. Thanks to the work of several laboratories there is now good evidence that in many cases the linkage between transport systems is effected by a circulation of protons across the membrane as proposed in Mitchell's chemiosmotic theory: Metabolic pathways bring about the extrusion of protons and thus generate a gradient of pH and electrical potential across the membrane; this proton-motive force is the immediate energy donor for many transport systems. However, we also recognize a growing number of systems that utilize ATP, or an unidentified metabolite thereof, by a mechanism which is not understood. Studies are to be continued with two complementary systems, Streptococcus faecalis and membrane vesicles of Escherichia coli. Primary emphasis will be on the molecular basis of ATP requirement for the transport of potassium, phosphate and certain amino acids. If time permits we hope to explore the mechanism of osmotic adaptation in bacteria and factors that regulate the cytoplasmic pH. BIBLIOGRAPHIC REFERENCES: Altendorf, K., Hirata, H. and Harold, F.M. (1975). Accumulation of lipid-soluble ions and of rubidium as indicators of the electrical potential in membrane vesicles of E. coli. J. Biol. Chem. 250:1405-1412. Harold, F.M. and Spitz, E. (1975). Accumulation of arsenate, phosphate and aspartate by S. faecalis. J. Bacteriol. 122:266-277.